In one known form of temperature controlled regulator as disclosed for example in the U.S. Pat. No. 3,561,482, the valve housing is provided with hot and cold fluid inlet ports having a mixing chamber, and having a temperature sensing device in the outlet operative to conduct to a valve actuating motor a pressure which is between the pressure in the cold fluid inlet and the downstream pressure in the valve outlet. Such variable pressure acting on one side of the motor in opposition to the fluid pressure in said cold fluid inlet is operative to increase the flow of hot fluid and to decrease the flow of cold fluid when the temperature sensed by the thermostat decreases and to decrease the flow of the hot fluid and to increase the flow of cold fluid when the temperature sensed by the thermostat increases thereby to maintain a predetermined temperature at the valve outlet in which the hot and cold fluids are mixed.